The present invention relates, in general, to optical devices and, more particularly, to optical coupling of an opto-electronic transmitter and receiver.
Opto-isolators are used where it is desirable to electrically isolate two sections of an electronic circuit, for example, to provide improved noise isolation or to prevent user contact with a high-voltage power supply. One prior opto-isolator provides a light-emitting diode (LED) and photo-detector on electrically separated halves of a leadframe so that the LED and the photo-detector are in a common plane. An optically transparent material surrounds the LED and photo-detector, and this material is disposed in a cavity that is surrounded by an optically reflective packaging material. Light from the LED is reflected off of the reflective walls of the cavity onto the photo-detector.
A problem with this prior opto-isolator is that light strikes the photo-detector only after typically several reflections off the surface of the cavity's reflective wall. As a result of this stray light scattering, a large percentage of the light from the LED never strikes the active surface of the photo-detector, and the efficiency of the opto-isolator is greatly decreased. Accordingly, it is desirable to have an opto-isolator in which stray scattering of light from the LED is significantly reduced so that the efficiency of the opto-isolator is improved.